Feeder for solid materials



Oct 17, 19 G. T. HUTCHISON FEEDER FOR SOLID MATERIALS Filed Jan. 13,1964 United 3,341,741 Patented Get. 17, 196? 3,347,741 FEEDER FDR SOLIDMATERIALS Gibson T. Hutchison, Maple Glen, Pa., assignor to Crane Co.,Chicago, Ill., a corporation of Illinois Filed Jan. 13, 1964, Ser. No.337,458 3 Claims. (Cl. 162--241) ABSTRACT OF THE DISCLOSURE An apparatusfor feeding wood chips to a pulp digester comprising a transfer chamberand means for equalizing the pressure in the transfer chamber and thedigester. There is also provided means for applying a vacuum to thetransfer chamber for removing the air from within the intricacies andbetween the fibers of the wood chips while contained within the transferchamber.

This invention relates generally to feeders for solid materials of thefree flowing type.

While the invention is applicable broadly to feeding of such materialsfrom a supply thereof to a vessel in which the pressure is greater thanthe pressure of the supply, it will be described hereafter as it isapplicable specifically to the paper industry for the feeding of woodchips to a pulp digester.

In the paper industry,'pulp digesters in the past have involved a batchprocess in which the digester, a large tank, is filled with wood chips,a cooking liquor is added and the batch is heated at a cookingtemperature. At the end of the cooking cycle, the chips and liquor areblown down to a blow tank wheresteam flashes to atmosphere or otherpoints in the process, and the digester is emptied in preparation foranother charge. Obviously, a continuous process for pulp digestion wouldhave many advantages over the batch process, such as greater output byreason of the elimination of the heat up and blow down steps, improvedquality by reason of better process control, and the adaptability of theprocess to automation. One of the main problems encountered in theprovision of a satisfactory continuous digestion operation is themetering and is at an elevated pressure and temperature. Prior feedingdevices for such an operation have involved the use of a screw feeder, arotary valve, or combinations thereof. However, such devices have notproved to be entirely satisfactory. For example, drawbacks of rotaryvalves are that they jam up, it is is difiicult to control leakage, andthere are excessive wear areas.

In accordance with the present invention there is provided a novelfeeder which comprises a transfer chamber or lock positioned between thesupply of the wood chips and the digester, a control valve forcontrolling flow of the solid material from the supply to the transferchamber and a control valve for controiling flow from the transferchamber to the digester. The control valves also serve to isolatevarious sections of the apparatus. Means are provided for equalizing thepressure in the transfer chamber and the digester prior to feeding ofthe material to the vessel, which pressure equalization permits a smoothflow of material. A feature of the feeding arrangement is that it may beused to meter the rate of chip feed. This is achieved by the provisionof a time control for the transfer operation in conjunction with thesize of the transfer chamber or lock.

The foregoing and other objects and features of the invention willbecome apparent from the following description in which the singlefigure is a diagram showing one form of apparatus provided in accordancewith this invention.

The single figure of the drawing illustrates the invention as applied toa feeder for a continuous pulp digester. It will be evident that theinvention is more generally useful, in that the solid material handledneed not be wood chips and the pressurized vessel need not be adigester. Nevertheless, for simplicity, the description will be phrasedconsistently with the feeding of wood chips to a continuous pulpdigester.

There is indicated at 2 a continuous digester, which may be ofconventional construction. During operation, the digester 2 ismaintained at an elevated cooking temperature and pressure condition.Digester 2 has an inlet connection 4 in the top thereof. Mounted abovethe digester 2 in alignment with the inlet connection 4 is a bin 6containing a supply of wood chips which are to be fed to the digesterand having an open bottom end. In vertical alignment between the openbottom end of the bin 6 and the 8 is connected to the bottom of the bin6 for receiving flow therefrom and the lower conduit 12 is connected tothe inlet connection 4 for flow of solid material into the digester.

A valve 14 is provided in conduit 8 for controlling the flow of solidmaterial therethrough. Valve 8 may be of any suitable type, butpreferably is of a type of gate valve used in the art for pulp stockflow control and having nozzles arranged to direct jets of liquid orsteam to clear the seatin and sealing surfaces. Conduit 12 is providedwith a similar valve 16 for controlling flow therethrough and closingoff or opening this conduit. A transfer chamber or lock is defined inthe vertical conduits between the upper and lower valves 14 and 16.Valves 14 and 16 are operated by suitable valve actuating power means 18and 20, respectively, and are provided with nozzles 22 and 24,respectively, to clear the seating surfaces. Nozzles 22 and 24 aresupplied with steam or liquid 28 and control valves 30 and 32,respectively.

Means are provided for equalizing the pressures in the transfer chamberand the digester 2. Such means comprises a line 34 connected to theupper end of the transfer chamber, a line 35 connected between line 34and the upper end of the digester 2 and a pressure equalization valve 38connected in line 36 for controlling flow therethrough.

Means are Such be described as follows:

The first step in the cycle is that of filling the transfer chambercontained in the enclosed space between the valves 14 and 16. In thefilling step, only the inlet valve a 14 and the vent valve 40 are open,all the other valves being closed. Accordingly, the wood chips containedin the bin 6 will fall into the transfer chamber by gravity flow to fillthe space between the valves 14 and 16. During the filling step, thetransfer chamber is vented to atmosphere through the vent valve 40whereby both the bin 6 and the transfer chamber are at atmosphericpressure.

The next step is to close the valve 14 to trap the chips within a sealedtransfer chamber or look. The closure is effected by operation of thevalve actuating means 18 which moves a valve member to close the passagethrough conduit 8. During the closing movement of the valve member, ventvalve 40 and control valve 34) are the only valves which are open. Theopen condition of control valve 30 permits the flow of high pressureliquid or steam from source 26 through line 28 to the nozzles 22.Accordingly, jets of fluid are directed to clear the valve gate andseat.

The next step is that of evacuation of the transfer chamber. In thisstep only the evacuation valve 46 is open Wherefore the vacuum source 42is in communication with the transfer chamber through lines 44, 36 and34. The application of a vacuum to the transfer chamber reduces thepressure appreciably to below atmospheric pressure. This causes the airwithin the intricacies and between the fibers of the wood chips to beforced out, making easier the penetration of the heating steam and/ orcooking liquor in the subsequent steps of pulp digestion. The evacuationstep may be optimized by reducing the pressure below the vapor pressurecorresponding to the temperature of the chips so that water within thechips is vaporized, resulting in maximum expulsion of air from withinthe chips.

The next step is to equalize the pressures in the transfer chamber andthe digester, the latter being at a pressure greater than that in thetransfer chamber. In this step, all the valves are closed with theexception of the pressure equalization valve 3% which is open to providecommunication through line 36 between the transfer chamber and thedigester 2. This communication between the two chambers permits pressureequalization to take place. It is to be noted that some chip preheatingtakes place in the transfer chamber during this step, the degree ofpreheating being dependent upon the length of time allocated to thisstep. If desired, time greater than that required for pressureequalization may be taken.

After the pressure equalization step is completed, it is time to openthe valve 16 to provide communication between the transfer chamber andthe vessel. The valve opening is effected by operation of the valveactuating means 20 which moves a valve member to open the passagethrough conduit 12. During opening movement of the valve member, thepressure equalization valve 38 and the control valve 32 are the onlyvalves which are open. The open condition of control valve 32 permitsthe flow of high pressure liquid or steam from source 26 through line 28to the nozzles 24 whereby jets of fluid are directed to clear the valvegate and seat.

Upon the opening of valve 16, the feeding of the chips from the transferchamber to the digester takes place. In this step, pressure equalizationvalve 38 and transfer valve 16 are open. The feed is by gravity flowfrom the transfer chamber downwardly through conduit 12 and inletconnection 4 into the digester. The feed is smooth by reason of theequalized pressure condition. If desired, the valve 52 may also beopened at this time to introduce cooking liquor into the transferchamber.

After all the chips have dropped into the digester, the next step is toclose valve 16. This closure is effected by operation of the valveactuating means 20 and, as in the case of the opening of this valve, thecontrol valve 32 is open to permit the introduction of jets of fluid forclearing the valve gate and seat. Also, the pressure equalization valve38 is open in this step.

After the valve 16 is closed completely, the transfer chamber is sealedat both ends. The next step is to relieve the pressure in the transferchamber, which pressure is at the elevated pressure of the digester. Inthis step all the valves are closed with the exception of the pressurerelief or vent valve 40. This valve 40' is left open a time sufficientto permit the pressure in the transfer chamber to drop to approximatelyatmospheric pressure.

The next step is to open the valve 14 in preparation for the feed ofchips into the transfer chamber. This opening is effected by operationof the valve actuating means 18 which moves a valve member to open thepassage through conduit 8. During this opening movement of the valvemember, vent valve 40 and control valve 30 are the only valves which areopen. The open condition of control valve 3!} permits the flow of highpressure liquid or steam from source 26 to the nozzles 22 whereby jetsof fluid are directed to clear the valve gate and seat.

The apparatus is now in condition for another filling of the transferchamber as discussed above. Accordingly, another charge of wood chipscontained in the bin 6 will fall into the transfer chamber by gravityflow to fill the space between the same.

The above description of the operation covers one cycle, and it will beapparent that this cycle may be repeated to provide a continuous feed ofchips to the digester at a desired rate. Preferably, the cycle may betime controlled with each step taking place a specified time intervaland the cycle being repeated at regulated intervals thereby metering thefeed rate. However, certain steps could be terminated in accordance withother measurements, such as, pressure, temperature or level.

It will be apparent that various of the above steps may be omitted whennot required for a specific process. Moreover, the cycle, steps andarrangements described above may vary from one installation to another,depending on the raw stock, the end product and the overall process.

A modification of the above cycle which will tend to prevent chips frombridging or arching in the bin would involve opening the valve 14 justbefore the pressure in the transfer chamber has reached atmospheric inits decay during the pressure relief step. This will cause a small puffor surge of gas from the transfer chamber into the bin through the valve14 to impose a slight shock or bump to the chips in the bin. This willminimize the possibility of the chips bridging in the bin.

In a modification of the apparatus, the pressure relief valve 34 ma I beconnected to any place where heat may be used at atmospheric pressure,as for example, to perform some type of preheating. This would make useof the high temperature of the gases in the transfer chamber after thepressure equalization step.

It will be apparent that the apparatus in accordance with the inventionhas several advantageous features. For example, by pressure relievingthe transfer chamber before connection to the bin, the apparatus avoidsan explosion into the hopper. Also, by evacuating the transfer chamberthrough the valve 48, the air is removed from the chips very effectivelysince the evacuation is performed on a relatively small space. Priorpulp digestion apparatus have not used the evacuation step because ofthe large evacuating equipment requirements and the structural designproblems involved in the evacuation of large vessels.

It is to be understood that various changes may be made in the detailsof the embodiment of the inventive concepts herein contained withoutdeparting from the scope of th invention. For example, while thepressure equalization in the described embodiment is achieved byconnecting the digester so that it serves as a source of pressureequalizing vapor, this vapor source could be a separate source at thesame pressure as the digester. Accordingly, it is not desired to belimited except as required by the following claims.

What is claimed is:

1. Apparatus for feeding wood chips to a pulp digester comprising a bincontaining a supply of wood chips, a

digester, the pressure in said digester being higher than that in saidbin, and means for transferring said chips from said bin to saiddigester including a transfer chamber, first conduit means connectingsaid bin and said transfer chamber, a valve in said first conduit meansfor controlling flow therethrough, second conduit means connecting saidtransfer chamber and said digester, a valve in said second conduit meanscontrolling flow therethrough, third conduit means for equalizing thepressure in said transfer chamber and said digester connected betweensaid digester and said transfer chamber and a valve for controlling flowthrough said last-mentioned conduit means, and means including a vacuumsource connected to said third conduit means and a valve between saidvacuum source and said third conduit means for controlling a vacuum tosaid transfer chamber to reduce the pressure therein appreciably belowatmospheric pressure so as to remove the air from within the intricaciesand between the fibers of the wood chips within said transfer chamber.

2. Apparatus according to claim 1 comprising means for venting saidtransfer chamber to atmosphere.

References Cited UNITED STATES PATENTS 691,975 1/1902 Schaaf 162-246 X1,704,728 3/1929 De Cew 162-53 X 2,582,054 1/1952 Michon 162-246 X2,858,212 10/1958 Durant 162-237 3,076,739 2/1963 Nettle 162-173,190,509 6/1965 Kirchhoefer 214-17.4 3,215,587 11/1965 Guerrieri 162-53X S. LEON BASHORE, Acting Primary Examiner. HOWARD R. CAINE, Examiner.

1. APPARATUS FOR FEEDING WOOD CHIPS TO A PULP DIGESTER COMPRISING A BINCONTAINING A SUPPLY OF WOOD CHIPS, A DIGESTER, THE PRESSURE IN SAIDDIGESTER BEING HIGHER THAN THAT IN SAID BIN, AND MEANS FOR TRANSFERRINGSAID CHIPS FROM SAID BIN TO SAID DIEGSTER INCLUDING A TRANSFER CHAMBER,FIRST CONDUIT MEANS CONNECTING SAID BIN AND SAID TRANSFER CHAMBER, AVALVE IN SAID FIRST CONDUIT MEANS FOR CONTROLLING FLOW THERETHROUGH,SECOND CONDUIT MEANS CONNECTING SAID TRANSFER CHAMBER AND SAID DIGESTER,A VALVE IN SAID SECOND CONDUIT MEANS CONTROLLING FLOW THERETHROUGH,THIRD CONDUIT MEANS FOR EQUALIZING THE PRESSURE IN SAID TRANSFER CHAMBERAND SAID DIGESTER CONNECTED BETWEEN SAID DIGESTER AND SAID TRANSFERCHAMBER AND A VALVE FOR CONTROLLING FLOW THROUGH SAID LAST-MENTIONEDCONDUIT MEANS, AND MEANS INCLUDING A VACUUM SOURCE CONNECTED TO SAIDTHIRD CONDUIT MEANS AND A VALVE BETWEEN SAID VACUUM SOURCE AND SAIDTHIRD CONDUIT MEANS FOR CONTROLLING A VACUUM TO SAID TRANSFER CHAMBER TOREDUCE THE PRESSURE THEREIN APPRECIABLY BELOW ATMOSPHERIC PRESSURE SO ASTO REMOVE THE AIR FROM WITHIN THE INTRICACIES AND BETWEEN THE FIBERS OFTHE WOOD CHIPS WITHIN SAID TRANSFER CHAMBER.